def EU2C(E,U,T=0):
'''
Get the expectation matrix in k-space.
Parameters:
:E,U: ndarray, the eigenvalues and eigenvectors defined on real space.
ndim(E)>=2 and ndim(U)=ndim(E)+1.
Return:
ndarray, the expectation matrix(the expectation mesh of <ck^\dag,ck>)
'''
assert(ndim(E)>=1 and ndim(U)==ndim(E)+1)
fm=fermi(E,T=T)
C=bcast_dot((U.conj()*fm[...,newaxis,:]),swapaxes(U,-1,-2))
return C
def C2H(C,T=1.):
'''
Get the entanglement hanmiltonian from expectation matrix.
Parameters:
:C: ndarray, the expectation matrix.
:T: float, the temperature.
Return:
ndarray, the hamiltonian.
'''
CE,CU=eigh(C)
print 'Checking for the range fermionic occupation numbers, min -> %s, max -> %s.'%(CE.min(),CE.max())
assert(all(CE>0) and all(CE<1))
H=bcast_dot(CU.conj()*(log(1./CE-1)*T)[...,newaxis,:],swapaxes(CU,-1,-2))
return H
